A member of staff at Charles de Gaulle airport, Paris, wearing a face mask and visor.
Photograph: Ian Langsdon/AP

Face visors and shields could protect workers who have close contact with others against infection from Covid-19, but may not prevent the wearer spreading the virus, experts have said.

Linda Bauld, a professor of public health at the University of Edinburgh, said research was needed into the alternative forms of face protection before they could be recommended for general use.

Visors or shields are worn by medics in addition to masks for risky procedures in hospitals, and UK stores including Co-op, Marks and Spencer and Waitrose have offered them to their staff. A viewpoint published in the Journal of the American Medical Association (JAMA) last month suggested they “may provide a better option” than homemade cloth coverings as advocated in the UK and several US states.

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Coronavirus: should everyone be wearing face masks?

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People over 60 or with health issues should wear a medical-grade mask when they are out and cannot socially distance, according to new guidance from the World Health Organization, while all others should wear a three-layer fabric mask.

The WHO guidance, announced on 5 June, is a result of research commissioned by the organisation. It is still unknown whether the wearers of masks are protected, say its experts, but the new design it advocates does give protection to other people if properly used.

The WHO says masks should be made of three layers – with cotton closest to the face, followed by a polypropylene layer and then a synthetic layer that is fluid-resistant. These are no substitute for physical distancing and hand hygiene, it says, but should be worn in situations where distancing is difficult, such as on public transport and at mass demonstrations.

The WHO has been reluctant to commit to recommending face coverings, firstly because the evidence on whether they offer any protection to the public is limited and – more importantly – because it was afraid it would lead to shortages of medical-grade masks for health workers.

However, Bauld said she was sceptical. “The reason for having a visor which would cover the upper half of your face would be if you’re regularly coming into contact with the public at closer range, and you might be exposed to somebody who is emitting those small droplets that we’re all aware are very efficient at carrying the virus,” she said.

“So I could see how in some retail settings and other environments they wish to do that, but I don’t think there’s any strong evidence that they’re something the public should be wearing on a routine basis. The key thing is to cover the mouth and the nose.

“The face coverings that people are being encouraged to use, for example, on public transport is not to protect the wearer, but to protect other people. Whereas the visor and harder material is clearly to protect the wearer from coming into contact with others at those droplets.”

While there have been several studies in relation to face masks, albeit often with contrary conclusions, there has not been the same research into face shields or visors. The JAMA commentary referenced a study which found that shields worn by a test subject within 1.8 metres of a cough reduced inhaled influenza virus by 92%, although this protective effect reduced after the cough had dispersed for 30 minutes.

Bill Keevil, a professor of environmental healthcare at the University of Southampton, said the advantages of shields include that they protect the eyes, are easier to put on and wash, prevent people touching their face, and are also better for people with breathing difficulties, such as asthma, who have been told not to wear face coverings in the UK.

“You can see how, in a way, it would give better protection for the wearer and it may – I just say may – help reduce transmission to others, because whatever you produce is not projecting a long way from your face,” he said.

Additionally, face shields and visors appear to be easier to make than high-specification medical and surgical masks, as evidenced by a number of UK universities manufacturing them, including through the use of 3D printing.

In the US, companies such as Amazon, Apple, Nike and General Motors have been making them, with Amazon saying that after the needs of healthcare workers are fulfilled, they will be available for purchase by all customers.

But Bauld stressed that members of the public could easily make improvised masks at home. “The basic face coverings we’re encouraging people to use can be made by anybody with any fabric … which is why the public are being encouraged to use their own or make their own rather than order them off some website where they’re needed for other settings,” she said.

While acknowledging some positive elements of visors and shields, she said it was noticeable that, in countries ahead of the UK in infection control such as Hong Kong and Singapore, plastic visors are not seen. “It’s not happening, right?” she said. “So this is additional protective equipment for specific environments.

However, Keevil thought it was possible visors could catch on. “It’s a sort of societal change thing, isn’t it? As people start to see these then some people might start thinking: ‘Why am I messing around with a homemade cloth cover?’,” he said.